NRAS and fibrosarcoma: KRAS and NRAS (Neuroblastoma RAS viral oncogene homolog) encode closely related small GTPases (Guanosine Triphosphatases) that function as binary molecular switches within the RAS–RAF (Rapidly Accelerated Fibrosarcoma)–MEK (Mitogen-Activated Protein Kinase Kinase)–ERK (Extracellular Signal-Regulated Kinase) mitogen-activated protein kinase (MAPK) cascade and additionally modulate PI3K (Phosphatidylinositol 3-Kinase)–AKT (Protein Kinase B) signaling (Figure 4).